[PATCH v4 2/8] migration/multifd: add get_iov_count in the multifd method

[Yuan Liu <yuan1.liu@intel.com>]

the new function get_iov_count is used to get the number of
IOVs required by a specified multifd method

Different multifd methods may require different numbers of IOVs.
Based on streaming compression of zlib and zstd, all pages will be
compressed to a data block, so an IOV is required to send this data
block. For no compression, each IOV is used to send a page, so the
number of IOVs required is the same as the number of pages.

Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
Reviewed-by: Nanhai Zou <nanhai.zou@intel.com>
---
 migration/multifd-zlib.c | 18 +++++++++++++++++-
 migration/multifd-zstd.c | 18 +++++++++++++++++-
 migration/multifd.c      | 24 +++++++++++++++++++++---
 migration/multifd.h      |  2 ++
 4 files changed, 57 insertions(+), 5 deletions(-)

diff --git a/migration/multifd-zlib.c b/migration/multifd-zlib.c
index 012e3bdea1..35187f2aff 100644
--- a/migration/multifd-zlib.c
+++ b/migration/multifd-zlib.c
@@ -313,13 +313,29 @@ static int zlib_recv_pages(MultiFDRecvParams *p, Error **errp)
     return 0;
 }
 
+/**
+ * zlib_get_iov_count: get the count of IOVs
+ *
+ * For zlib streaming compression, all pages will be compressed into a data
+ * block, and an IOV is requested for sending this block.
+ *
+ * Returns the count of the IOVs
+ *
+ * @page_count: Indicate the maximum count of pages processed by multifd
+ */
+static uint32_t zlib_get_iov_count(uint32_t page_count)
+{
+    return 1;
+}
+
 static MultiFDMethods multifd_zlib_ops = {
     .send_setup = zlib_send_setup,
     .send_cleanup = zlib_send_cleanup,
     .send_prepare = zlib_send_prepare,
     .recv_setup = zlib_recv_setup,
     .recv_cleanup = zlib_recv_cleanup,
-    .recv_pages = zlib_recv_pages
+    .recv_pages = zlib_recv_pages,
+    .get_iov_count = zlib_get_iov_count
 };
 
 static void multifd_zlib_register(void)
diff --git a/migration/multifd-zstd.c b/migration/multifd-zstd.c
index dc8fe43e94..25ed1add2a 100644
--- a/migration/multifd-zstd.c
+++ b/migration/multifd-zstd.c
@@ -304,13 +304,29 @@ static int zstd_recv_pages(MultiFDRecvParams *p, Error **errp)
     return 0;
 }
 
+/**
+ * zstd_get_iov_count: get the count of IOVs
+ *
+ * For zstd streaming compression, all pages will be compressed into a data
+ * block, and an IOV is requested for sending this block.
+ *
+ * Returns the count of the IOVs
+ *
+ * @page_count: Indicate the maximum count of pages processed by multifd
+ */
+static uint32_t zstd_get_iov_count(uint32_t page_count)
+{
+    return 1;
+}
+
 static MultiFDMethods multifd_zstd_ops = {
     .send_setup = zstd_send_setup,
     .send_cleanup = zstd_send_cleanup,
     .send_prepare = zstd_send_prepare,
     .recv_setup = zstd_recv_setup,
     .recv_cleanup = zstd_recv_cleanup,
-    .recv_pages = zstd_recv_pages
+    .recv_pages = zstd_recv_pages,
+    .get_iov_count = zstd_get_iov_count
 };
 
 static void multifd_zstd_register(void)
diff --git a/migration/multifd.c b/migration/multifd.c
index adfe8c9a0a..787402247e 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -209,13 +209,29 @@ static int nocomp_recv_pages(MultiFDRecvParams *p, Error **errp)
     return qio_channel_readv_all(p->c, p->iov, p->normal_num, errp);
 }
 
+/**
+ * nocomp_get_iov_count: get the count of IOVs
+ *
+ * For no compression, the count of IOVs required is the same as the count of
+ * pages
+ *
+ * Returns the count of the IOVs
+ *
+ * @page_count: Indicate the maximum count of pages processed by multifd
+ */
+static uint32_t nocomp_get_iov_count(uint32_t page_count)
+{
+    return page_count;
+}
+
 static MultiFDMethods multifd_nocomp_ops = {
     .send_setup = nocomp_send_setup,
     .send_cleanup = nocomp_send_cleanup,
     .send_prepare = nocomp_send_prepare,
     .recv_setup = nocomp_recv_setup,
     .recv_cleanup = nocomp_recv_cleanup,
-    .recv_pages = nocomp_recv_pages
+    .recv_pages = nocomp_recv_pages,
+    .get_iov_count = nocomp_get_iov_count
 };
 
 static MultiFDMethods *multifd_ops[MULTIFD_COMPRESSION__MAX] = {
@@ -998,6 +1014,8 @@ bool multifd_send_setup(void)
     Error *local_err = NULL;
     int thread_count, ret = 0;
     uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
+    /* We need one extra place for the packet header */
+    uint32_t iov_count = 1;
     uint8_t i;
 
     if (!migrate_multifd()) {
@@ -1012,6 +1030,7 @@ bool multifd_send_setup(void)
     qemu_sem_init(&multifd_send_state->channels_ready, 0);
     qatomic_set(&multifd_send_state->exiting, 0);
     multifd_send_state->ops = multifd_ops[migrate_multifd_compression()];
+    iov_count += multifd_send_state->ops->get_iov_count(page_count);
 
     for (i = 0; i < thread_count; i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
@@ -1026,8 +1045,7 @@ bool multifd_send_setup(void)
         p->packet->magic = cpu_to_be32(MULTIFD_MAGIC);
         p->packet->version = cpu_to_be32(MULTIFD_VERSION);
         p->name = g_strdup_printf("multifdsend_%d", i);
-        /* We need one extra place for the packet header */
-        p->iov = g_new0(struct iovec, page_count + 1);
+        p->iov = g_new0(struct iovec, iov_count);
         p->page_size = qemu_target_page_size();
         p->page_count = page_count;
         p->write_flags = 0;
diff --git a/migration/multifd.h b/migration/multifd.h
index 8a1cad0996..d82495c508 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -201,6 +201,8 @@ typedef struct {
     void (*recv_cleanup)(MultiFDRecvParams *p);
     /* Read all pages */
     int (*recv_pages)(MultiFDRecvParams *p, Error **errp);
+    /* Get the count of required IOVs */
+    uint32_t (*get_iov_count)(uint32_t page_count);
 } MultiFDMethods;
 
 void multifd_register_ops(int method, MultiFDMethods *ops);
-- 
2.39.3